The present invention relates generally to a display driver for a visual display. More particularly, the present invention relates to a circuit that provides drive signals to a display.
In general, it is desirous to provide more gray-scale capability to conventional flat panel displays. Gray-scale capability refers to the range from darkness to lightness for each pixel or element on a display. More gray-scale capability (e.g., more bits of gray-scale) are particularly important in avionic display systems and other high-definition viewing applications.
In conventional display systems, such as, liquid crystal display (LCD) systems, the brightness of each pixel or element is controlled by a transistor. The display includes a matrix of transistors, such as, thin film transistors (TFTs) arranged in rows and columns. A column line is coupled to the drain or source associated with each transistor in each column. A row line is coupled to each gate associated with the transistors in each row. A row of transistors is activated by providing a gate control signal to the row line. The gate control signal turns on each transistor in the row. Each transistor in the row provides an analog voltage associated with its column line to cause the pixel or element to emit a particular amount of light. Generally, a column driver circuit provides the analog voltage to the column lines so that the appropriate amount of light is emitted by each pixel or element. In conventional systems, the column driver circuit can typically provide approximately 8 or 16 levels of voltage at the column line (approximately 8 or 16 gray-scale levels).
Most conventional systems rely on a multiplexer-based column driver circuit to provide particular voltage levels. In such a scheme, a multiplexer includes a number of inputs, such as, 8 or 16 inputs. Each of the inputs is coupled to a different voltage level. Each voltage level is established by a resistive ladder or a resistive divider network or some other means. A control circuit selects a voltage level through the multiplexer and applies the voltage level as a gray-scale voltage signal to the column line. With such a scheme, one multiplexer is required for each column line. As displays include more columns, significantly more circuitry and power are required because a large multiplexer is required for each column.
Additionally, the multiplexer-based column driver not only requires larger size and more power when the gray-scale capability is increased, it is also more expensive. For example, in order to increase from a gray-scale capability having 16 levels to 64 levels, each multiplexer associated with each column must be increased in size, thereby increasing the size, cost, and power requirements of the driver circuit. Thus, there is a need for a display driver with increased gray-scale capabilities. Further still, there is a need for a column driver circuit for a liquid crystal display which provides more gray scales while using less power than conventional approaches which utilize a multiplexer-based structure. Further still, there is a need for a simplified column driver circuit for a liquid crystal display.
The present invention relates to a gray-scale voltage driver for a display having an array of transistors. The array includes a plurality of terminals receiving gray-scale voltage signals. The gray-scale voltage driver includes a plurality of analog memory devices, an analog voltage device, and a control circuit. The analog memory device have a memory input and a memory output. The memory output is coupled to a corresponding terminal of the terminals of the array. The analog voltage device has a voltage output. The voltage output is coupled to each memory input of the analog memory devices. The analog voltage device provides an analog voltage to the voltage output. The control circuit is coupled to the analog memory devices and controls the analog memory devices so the analog memory devices store the analog voltage at the memory input and provide the gray-scale voltage signals to the terminal.
The present invention further relates to a gray-scale voltage driver circuit for a liquid crystal display having an array of transistors arranged in at least a first row, a second row, a first column, and a second column. The transistors in the first column are coupled to a first column line. The transistors in the second column are coupled to a second column line. The gray-scale voltage driver circuit includes a first analog memory means for providing a first gray-scale voltage signal to the first column line, a second analog memory means for providing a second gray-scale voltage signal to the second column line, an analog voltage means for providing an analog voltage, and a control means for coordinating the provision of the analog voltage to the first and second analog memory means and the provision of the first and second gray-scale voltage signals.
The present invention still further relates to a method for providing gray-scale voltage signals to a liquid crystal display. The method includes providing a digital signal representative of an analog voltage signal, converting the digital signal to the analog voltage, storing the analog voltage in an analog memory unit, and providing the analog voltage from the analog memory device to the liquid crystal display as a gray-scale voltage signal.